1. Field of the Invention
The present invention relates to an improved asphaltic composition and its method of manufacture. More specifically, this invention is directed to an asphaltic composition having increased tensile properties which comprises asphalt, a mineral acid, a thermoplastic polymer and an unsaturated functional monomer.
2. Discussion of Related Art
Asphalt is a bituminous material resulting from the distillation of crude oil. Typically, asphalt is derived from the bottoms of a vacuum distillation tower and has an atmospheric boiling point of at least 400.degree. C. Because it is hydrophobic and has good adhesiveness and weatherability, asphalt has been used widely as a binder in paving materials and as a coating for roofing shingles.
However, the properties of asphalt are known to vary with temperature. For example, at low temperatures (i.e. temperatures below about 0.degree. C.), it becomes hard and brittle, but will soften and creep at high temperatures (i.e. temperatures above about 40.degree. C.). Accordingly, various methods have been suggested for improving the performance of asphalt at these temperature extremes.
In one method, asphalt's tendency to soften and creep at high temperatures is decreased when the asphalt is polymerized by undergoing oxidative dehydrogenation in which the said asphalt is contacted with an oxygen-containing gas (usually air) at temperatures ranging between about 200.degree. C. and about 300.degree. C. for a period of time ranging between about 6 and about 24 hours. This procedure is described in detail by L. W. Corbett in Bituminous Materials: Asphalts, Tars and Pitches, Interscience Publishers, New York (1965) and by E. B. Barth in Asphalt Science and Technology, Gordon and Breach Science Publishers, New York (1968), the disclosures of each being incorporated herein by reference.
In another method, a mineral acid such as phosphoric acid is added to the asphalt to improve its thermal stability, ductility and adhesiveness relative to straight-run asphalts (i.e. residues from the vacuum distillation of crude oil) which have undergone oxidative dehydrogenation.
Yet another way to decrease asphalt's tendency to soften and creep at high temperatures (as well as to improve its low temperature flexibility and solid-like properties) is to add thermoplastic elastomers such as styrene-butadiene-styrene ("SBS") block copolymers. The addition of such polymers serve to modify asphalt for additional applications, such as roofing sheets, adhesives and coatings. For example, German Patent No. 2,255,173 discloses the addition of thermoplastic block copolymers (such as SBS copolymer) to straight-run asphalt after which small amounts of mineral acid (such as phosphoric acid or hydrochloric acid) are added to stabilize the resulting product, which has higher elasticity and greater range of plasticity than straight-run asphalts. However, no mention is made of contacting the asphalt with an oxygen-containing gas.
In another example, Japanese Patent No. 51-53522 discloses an asphaltic composition having improved strength due to the addition of a natural or synthetic rubber (e.g. styrene-butadiene copolymer) and an unsaturated acid, including the anhydrides of said acid. The asphaltic material may be straight-run asphalt, semi-blown asphalt, blown asphalt, tar, pitch or mixtures thereof. In addition, Japanese Patent No. 56-115354 teaches pre-reacting SBS polymer with unsaturated dicarboxylic acids and derivatives thereof (such as maleic acid, fumaric acid, chloromaleic acid, itaconic acid, cis-4-cyclohexene-1,2-dicarboxylic acid, endo-cis-bi-cyclo (2,2,1)-5-heptane-2,3-dicarboxylic acid, and acid anhydrides, esters, amides, imides, etc. of the dicarboxylic acid) and adding the mixture thus formed to asphalt to improve its adhesiveness, strength and deformation resistance. The resulting product is useful as a pavement structure for roadways which experience heavy repetitive loads. Among the preferred dicarboxylic acids and derivatives thereof are maleic acid, fumaric acid, and maleic anhydride. However, neither Japanese patent teaches or suggests contacting the asphalt with a mineral acid prior to addition of the polymer.
Accordingly, none of the foregoing references, alone or in combination, teach or suggest applicant's composition nor the particular method by which said composition is formed.